1. Technical Field
This invention relates to methods for bonding or adhering substrates using silicone rubber. More specifically, with regard to the bonding of two substrates using a silicone rubber composition comprised of a thermal-crosslinking component and a moisture-crosslinking component, the present invention relates to such silicone rubber bonding methods that are capable of substantially reducing the setting time and firmly bonding the substrates.
2. Prior Art
Moisture-crosslinking silicone rubber compositions can be crosslink at room temperature under the action of atmospheric moisture. When this type of composition is crosslinked and cured while in contact with a substrate, it is capable of yielding silicone rubber that tightly bonds a variety of substrates. As a result of these attributes, moisture-crosslinking silicone rubber compositions are used for adhesion applications in the very broadest range of industrial fields, for example, in the construction industry for adhering window glass to aluminum frames, for adhering window glass to window glass, and for adhering tile and mortar; in the automotive industry for sealing oil pans to engine bodies, for bonding automotive electrical circuit components on substrates, for bonding lamp bodies with lamp glass, and for bonding automotive glass to the automobile body; and in electrical/electronic sectors for adhering electronic circuit components to substrates.
Moisture-crosslinking silicone rubber compositions are exemplified by silicone rubber compositions comprised of silanol-terminated polydiorganosiloxane, curing catalyst, and organotrialkoxysilane, organotriacetoxysilane, or organotrioximosilane, and by silicone rubber compositions comprised of trialkoxysiloxy-terminated polydiorganosiloxane, curing catalyst, and organotrialkoxysilane, organotriacetoxysilane, or organotrioximosilane, such as shown in Japanese Patent Application Laid Open [Kokai or Unexamined] Numbers Sho 61-247756 [247,756/1986], published Nov. 5, 1986, and Sho 62-252456 [252,456/1987], published Nov. 4, 1987, both assigned to the same assignee as the present application.
However, crosslinking in moisture-crosslinking silicone rubber compositions develops from those regions in contact with atmospheric moisture, and as a result long periods of time are required for crosslinking in deep sections. More specifically, the corresponding requirement for long setting times is a drawback associated with the use of this type of composition in continuous processes for bonding two substrates. The setting time is the time required for crosslinking to develop to such a degree that the adherends can tolerate transport and other handling and can be transferred to ensuing processes. In contrast, thermal-crosslinking silicone rubber compositions can be rapidly crosslinked even in deep sections by heating and are therefore used as molding materials, potting materials, and the like.
Thermal-crosslinking silicone rubber compositions are exemplified by addition reaction-crosslinking silicone rubber compositions comprised of a polydiorganosiloxane that has at least 2 alkenyl groups in each molecule, an organopolysiloxane that has at least 2 silicon-bonded hydrogen in each molecule, and a hydrosilylation catalyst. Peroxide-crosslinking silicone rubber compositions comprised of polydiorganosiloxane and organoperoxide are another example of thermal-crosslinking silicone rubber compositions.
However, these thermal-crosslinking silicone rubber compositions generally have poor adhesive properties. In the case of continuous operations in which two substrates are bonded using this type of composition, the adhesion process is complicated by the resulting requirement for a preliminary primer treatment of the substrates.
In an effort to improve the adhesive properties of thermal-crosslinking silicone rubber compositions, silicone rubber compositions comprised of a thermal-crosslinking component and a moisture-crosslinking component have been proposed. One example of this type of silicone rubber composition is a silicone rubber composition prepared by blending a moisture-crosslinking silicone rubber composition comprised of silanol-terminated polydiorganosiloxane and organotriacetoxysilane to homogeneity with a thermal-crosslink-ing silicone rubber composition comprised of organopolysiloxane and organoperoxide as shown by Przybyla in U.S. Pat. No. 4,034,140, issued Jul. 5, 1977. Another example is a silicone rubber composition comprised of silanol-terminated polydiorgano-siloxane, amidosilane, and organoperoxide as shown by Homan et al in U.S. Pat. No. 4,614,760, issued Sep. 30, 1986.
However, several drawbacks still occur during the continuous bonding of two substrates with silicone rubber compositions composed of a thermal-crosslinking component and a moisture-crosslinking component. Specifically, long setting times and an unsatisfactory adhesion between substrate and silicone rubber occur in the case of conventional adhesion methods, for example, application of the composition to substrate followed by formation of silicone rubber by heating the composition.
The inventor carried out extensive investigations in order to solve the problems described above and achieved the present invention as a result.